The invention relates to a contact member for covering structures that come into contact with glass objects during their moulding process: in general, during the transport of the glass throughout the entire process, and more in particular also during the phase involving the actual moulding and tempering of the moulded glass.
The contact member or covering according to the invention can for example be used to cover the support rings (pressure and tempering rings) used for shaping and/or tempering car glass sheets, i.e. windows for vehicles. In addition, the covering can also be used for covering the means by which the glass (or glass object) is lifted to move it, for example, between the different phases of the forming process. The actual moulding means, such as for example the pressure moulds, can also be covered with the covering. These applications will be explained below, with emphasis on the numerous advantages offered by the use of a covering according to the invention in the different situations.
In essence there are three basic process phases or steps that can be distinguished in the glass forming process as a whole: the actual shaping of the glass, in particular of glass plates, the transport, and the tempering of the glass after it has been shaped.
Different processes are known. The glass is heated in an oven to the shaping temperature. The shaping itself then occurs, for example, by pressing the glass using a form or mould and a ring, or using two moulds that are mounted either horizontally or vertically. Next, the glass--often supported by a ring--can be transferred to the tempering zone, where the glass, whether supported by the same ring or not, is cooled by air.
Another process consists in producing the forming or shaping of the glass through the mere action of gravity on the hot glass, which again is supported by a ring. This method is referred to as "gravitational bending" or "gravitational sag" method.
In what follows, the pressure and tempering rings referred to above will be designated hereafter in general as support rings. The term "support ring" should therefore be broadly interpreted in the present description: it relates to any ring which comes into contact with the glass, even if only for a brief time and no matter what the position of the ring may be in relation to the glass.
The support rings are often provided with a covering to avoid the adverse effects of direct contact between the glass and the steel ring. Such coverings are subject to a great diversity of requirements. For example, the covering must be sufficiently thermally insulating, and during the hot moulding process the covering should leave as few imprints or marks on the glass as possible, and preferably none at all. Moreover, the (perforated) covering should have a large air permeability in order not to shield the glass too much during tempering.
The support ring is conventionally covered, for example, with one or more layers of metal mesh, as described in the American U.S. Pat. No. 3,741,743. Although the ring is often serrated/toothed or perforated in order not to shield the glass too much from the air during tempering, the air permeability of the covered ring is often still insufficient because the perforations or the serrated gaps are closed by the covering. In addition, the deformability and thermal resistance of the aforementioned meshes also turn out to be insufficient in practice. Thus the covering can be fitted only with great difficulty to certain complex mould forms and only a brief glass/ring contact can be permitted. However the shapes that manufacturers want to impart to glass are becoming increasingly complex, so that--as a consequence--the required contact time between glass and ring during pressing is increasing.
In the European patent EP 0312439 a metallic covering is proposed which is constructed of oriented metal fibres and has an essentially mesh-shaped structure. Thus, for example, a woven or knitted metal fibre cloth is used which is fixed on the (perforated or serrated) support ring, either directly on the support ring or with a metal mesh interbetween.